A new optical method for angle measurement based on total-internal-reflection heterodyne interferometry is presented. In this method, heterodyne interferometry is applied to measure the phase difference between s and p polarization states at total internal reflection. This phase difference depends on the angle of incidence. Hence, small-angle measurement can be performed only by evaluating this phase difference. The validity of the method is demonstrated, and it has a measurement range of 10 deg. Its resolution depends on the angle of incidence; the best resolution is 8×10−5 deg. © 1997 Society of Photo-Optical Instrumentation Engineers.